There are some solder tasks in which a conductor is to be bonded to another element which are very difficult to accomplish because of a need for exact placement of the conductors, or because of a need to limit the amount of solder that is employed, or simply because of the small physical size of the elements that are to be bonded. The problem is particularly severe in the bonding of conductor wires to a piezo-electric crystal. The wires that are bonded to such crystals may be employed as electrical conductors or to provide a means for mounting the crystal, or to both. Sometimes the wires are laid with a portion of their ends flat against the surface of the crystal, and sometimes they must be butt-bonded to the crystal. Butt-bonding is particularly difficult. The bond is usually made exactly at a nodal point, and it must be made with a minimum solder. In one example, the crystal employed in certain crystal controlled wrist watches is formed as a rectangular bar which oscillates such that there are two nodal points along its length. In one version, two wires are bonded to the same side of the bond at each of the nodal points. In another version, a second pair of wires is bonded at the nodal points at the opposite side of the crystal.
It has been the practice to hold the crystal in a fixture at which a source of heat is available. Conductor wires are picked up one at a time. An end is dipped into flux, and then into a molten solder pot so that the end of the wire is tinned. That wire is then placed in a fixture in line with the point on the crystal to which it is to be bonded. Thereafter, some biasing means is employed for pushing the wire into engagement with the crystal. The plating on the crystal surface and the wire tinning are heated sufficiently so that solder flows to the plating on the crystal surface. Upon removal of the heat, the solder solidifies and the bond is completed.
While the methods and the apparatus that have been employed to perform that task have produced satisfactory products, they have not permitted anything approaching mass production. Labor costs, non-uniformity, and the chance for error have been great. It is the purpose of this invention to provide apparatus which overcome that difficulty in large degree.